Dendritic Morphology of Pyramidal Neurons Across the Visual Stream: A Direct Comparison of Chimpanzees and Humans

1Department of Anthropology, Center for the Advanced Study of Hominid Paleobiology, The George Washington University, 2Neuroscience Institute, Georgia State University, 3Department of Psychology, Colorado College

The morphology of pyramidal neurons in human and chimpanzee cerebral cortex has previously been demonstrated to increase in dendritic complexity and spine density in cortical regions of increasing neural integration, such as prefrontal cortex. The role of brain size scaling on the elaboration of dendritic arbors has been difficult to interpret, however, in part because of the wide diversity of regions previously studied. The present study examines variation in the dendritic morphology of pyramidal neurons between humans and chimpanzees within a functionally-related processing stream of ventral visual regions. Cortical samples from three different visual regions representing increasing integration (V1, V2, and fusiform gyrus) from two chimpanzees and two humans were stained with the rapid Golgi technique. Ten neurons from each region of each individual were traced with Neurolucida software, for a total of 120 neurons.

The following measures were analyzed: soma area, total dendritic length, mean dendritic segment length, dendritic segment count, dendritic spine number, and dendritic spine density. Univariate analyses indicated that many measures of dendritic complexity increase along the processing hierarchy in both species; however, a repeated measures ANOVA revealed there were no significant species differences in the pattern of regional variation according to any of these measures (F=.005≤x≤2.035, P=.077≤x≤.975). These findings suggest that the pyramidal neuron morphology underlying neural integration along the levels of the ventral visual stream of the neocortex is similar in humans and chimpanzees.

This work was supported by the James S. McDonnell Foundation (22002078).